diff --git a/src/path.test.ts b/src/path.test.ts
index 561c71a..0076d56 100644
--- a/src/path.test.ts
+++ b/src/path.test.ts
@@ -278,6 +278,12 @@ Deno.test("withExtname", () => {
   path = path.withExtname(".txt");
   assertEquals(path.basename(), "other.txt");
   assertEquals(path.extname(), ".txt");
+  path = path.withExtname("");
+  assertEquals(path.basename(), "other");
+  assertEquals(path.extname(), undefined);
+  path = path.withExtname("txt");
+  assertEquals(path.basename(), "other.txt");
+  assertEquals(path.extname(), ".txt");
 });
 
 Deno.test("withBasename", () => {
diff --git a/src/path.ts b/src/path.ts
index da054ae..59aa57a 100644
--- a/src/path.ts
+++ b/src/path.ts
@@ -380,7 +380,7 @@ export class PathRef {
   withExtname(ext: string): PathRef {
     const currentExt = this.extname();
     const hasLeadingPeriod = ext.charCodeAt(0) === PERIOD_CHAR_CODE;
-    if (!hasLeadingPeriod) {
+    if (!hasLeadingPeriod && ext.length !== 0) {
       ext = "." + ext;
     }
     return new PathRef(this.#path.substring(0, this.#path.length - (currentExt?.length ?? 0)) + ext);